In order to reduce the landing distance of a jet engine powered aircraft, as well as to increase the margin of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized on the jet engines in order to provide a braking thrust for slowing the aircraft. Thrust reversers typically function to reverse the direction of the jet thrust, from a normally rearward direction which is used for propelling an aircraft, to a forward direction for slowing or braking the aircraft. Typically, such thrust reversers are formed by thrust reverser "doors" which are capable of pivoting between two positions about an axis which is transverse and substantially diametrical with respect to the jet of the engine.
The first position finds the doors in a stowed position, out of the direct path of the exhaust blast of the engine. In this position, the doors form the exhaust nozzle of the gas turbine engine so that the thrust of the engine is directly rearward, thereby producing the forward thrust of the aircraft. In the second position, the doors are pivoted about the pivot axis to a transverse, blast deflecting or deployed position, to intercept and redirect the jet blast, and thereby produce the braking thrust for the aircraft when needed.
The thrust reversers are generally mounted on a fixed structure called a jet exhaust pipe. This jet exhaust pipe basically serves a dual role. In the forward thrust mode of operation of the jet engine, i.e. when the reverser doors are in the stowed position, the jet exhaust pipe forms a part of the envelope of the jet flow and is intended to ensure the best possible flow continuity with the inner skin of the thrust reverser doors.
In the reverse thrust operation, i.e. when the reverser doors are deployed, the jet exhaust pipe provides the throat of the nozzle, and defines as well the spacing distance from the thrust reverser doors.
Both of these functions of the jet exhaust pipe are important criteria for the proper operation of the jet engine. While in the forward thrust mode, a good flow continuity is essential to the proper forward thrust performance. In addition, the jet exhaust pipe must adequately define the throat area in reverse and the spacing distance in order to satisfy the operational compatibility requirements of the engine and of the thrust reverser when the thrust reverser is deployed.
Experience has shown that currently, thrust reversers tend to favor more the reversing function of operation. But this, unfortunately, is at the expense of the performance provided in the forward thrust mode of operation, meaning that performance degradation in the forward thrust mode is generally associated with the installation of thrust reversers. This is an unfortunate circumstance and a significant drawback, since the thrust reversers are only used for 15 to 30 seconds of a flight.
French patent 2,348,371 and U.S. Pat. No. 4,129,269 illustrate the lack of solid wall continuity between the jet pipe and the inner skin. While these patents assert that the resulting presence of the annular space improves the positioning of the reverser doors, experience has shown that the presence of such an annular space, in the direct thrust mode, is not always beneficial, contrary to the suggestions in these patents. Only when the static pressure of the jet at the exit plane of the nozzle is less than the ambient pressure is the establishment, in operation, of a fluid wall beneficial to forward thrust performance.
Experience has also shown that the static pressure at the edge of the exhaust pipe is, in practice, always greater than the ambient pressure. In such case, the presence of an annular space is not desirable.
In other thrust reversers, the inner skin of the thrust reverser doors is shaped to fit in the stowed position in a complementary relationship with the jet exhaust pipe (U.S. Pat. No. 3,532,275). Such an arrangement is good for forward thrust performance, but is not efficient in reverse thrust performance as the reverse jet flow is not efficiently contained by the reverser doors. It is known that such reverser door configuration generates side spillages in reverse, which greatly affect the ground handling qualities of the aircraft with the reverser deployed, and also greatly reduce the decelerating force produced by the reverser.
Accordingly, a primary object of the present invention is to provide a thrust reverser which overcomes the disadvantages of known thrust reverser systems.
Another object of the invention is to provide a thrust reverser which, for forward thrust operation, does not modify the flow line of the jet of the engine. This means that when the reverser doors are stowed, the jet pipe ensures a perfect flow contour continuity with the inner skin of the reverser doors.
A further object of the invention is to provide a jet pipe which is arranged in such a manner that when the thrust reverser doors are commanded to deploy, the actuators which control the position of the reverser doors also open further the jet exhaust pipe in order to ensure proper throat area and spacing distance in reverse.
Still another object of the invention is to provide a thrust reverser capable of containing the reverse flux in order to avoid side spillages and ensure high retarding forces. According to the present invention, the flow lines of the jet exhaust pipe are completely similar to those of a non-reversing nozzle.
Although the system described in this invention can be installed on prior art thrust reversers such as those in French patent 2,348,371 or U.S. Pat. No. 4,129,269, it can also be beneficially used in combination with the invention described in copending application Ser. No. 798,213, now U.S. Pat. No. 5,176,340 issued Jan. 5, 1993, the specification of which is incorporated herein by reference, and which invention provides a planar exit nozzle.